This invention relates generally to sensor systems which are used to detect conditions for automatically opening a door. More particularly, the present invention relates generally to infra-red sensors employed in connection with controlling the operation of sliding door systems.
In sliding door sensor systems to which the invention relates, it is conventional to employ a traffic approach sensor unit on each side of the door as well as a safety sensor to monitor the area of the doorway threshold. Numerous types of systems have been advanced for use in the automatic opening and closing of doors. The traffic operate initiating function of the sensor system detects subjects approaching the doorway. The traffic sensor function normally involves the sensing of motion which may be accomplished by active or passive infra-red radiation or micro-wave radiation. The safety function of the sensor system normally involves the detection of the presence of a subject or foreign object within an immediate area of the threshold. Conventional presence detectors may employ infra-red radiation through beam, diffuse reflective infra-red radiation or ultrasound as detection media.
The electronic sensor technology is sufficiently advanced that motion sensor units are generally reliable in sensing the intrusion of a foreign object into the detection zone of a doorway while disregarding stationary objects in the zone. Nevertheless, false sensor readings do occur. A primary aim of all door sensor systems is reliability and safety. Consequently, safety sensor units are frequently employed in combination with traffic sensors to enhance safety. Conventional safety sensor units while generally providing adequate sensing capabilities, may occasionally exhibit operational deficiencies. Sensor units which employ an infra-red through beam ordinarily only cover a very narrow zone in front of the door threshold. The cooperative use of a motion sensor with an infra-red through beam may result in situations wherein an individual in the immediate vicinity or partially within a door threshold zone is not sensed, and the door is automatically allowed to close.
Because of the narrow zone limitations of infra-red through beam radiation, at least one safety sensor employs a diffuse reflective infra-red type sensor which is mounted above the door. The overhead door safety sensor ordinarily covers a larger detection zone than safety sensors mounted at other positions. However, the larger detection zone may also require processing logic which will compensate for the moving door panels so that a closing door will not reactivate or be sensed by the safety sensor. In addition, reactivation of the safety device may require triggering by the operate motion sensors which may not sense slow moving individuals under certain conditions - even when the individuals are relatively close to the door.
In U.S. patent application Ser. No. 048,634 filed on May 11, 1987 now U.S. Pat. No. 4,823,010 and assigned to the assignee of the present invention, a sliding door threshold sensor employs a plurality of infra-red transmitters. The transmitters emit infra-red radiation so as to define a detection zone which substantially encompasses the region above the threshold and the threshold vicinity at opposing sides of the threshold. The detection signal is processed for determining whether a foreign object is present in the detection zone. The processor logic includes means for compensating for the moving sliding doors. The transmitters and sensor circuitry is housed in a housing which is mounted above the threshold of the sliding door with four infra-red transmitters being employed to define overlapping regions of the detection zone.